There is growing evidence that individuals with mild cognitive impairment (MCI) are at increased risk for Alzheimer's disease (AD). Consequently, clinicians are faced with the question of how to properly evaluate subjects with a mild cognitive impairment. Recent studies suggest that oxidative stress may play a role in the pathogenesis of AD. The potential importance of oxidative stress mechanisms in disease pathogenesis was also suggested by a recent clinical trial of vitamin E and selegiline in subjects with moderate AD. This clinical trial indicates that treatment with vitamin E(2,000I.U./day) delayed time to important functional endpoints and suggests that vitamin E may slow clinical progression of disease in subjects with moderately severe AD. The present study will determine if this dose of vitamin E will delay progression to clinical AD in individuals with MCI. AD is associated with reduced concentrations of the neurotransmissor, acetylcholine, in the cerebral cortex. Acetylcholine is important for attention and memory, 2 cognitive functions impaired in AD. Cholinesterase inhibitors were developed in an attempt to increase acetylcholine levels in brain and improve related cognitive functions. Donepezil, a cholinesterase inhibitor, was approved by the FDA in 1996 as a symptomatic treatment for mild and moderate AD. This study will determine if donepezil treatment will delay progression to AD in MCI subjects. The specific aims of this study are:1) to evaluate the efficacy and safety of vitamin E (2,000 IU/day) or donepezil (10mg/day) compared to placebo for the prevention of Alzheimer's disease in individuals with mild cognitive impairment; 2) to evaluate the efficacy of vitamin E and donepezil on cognition in MCI subjects.